字符型转字符串型

char  a = 'a';
String str1 = a+"";
String str2 = String.valueOf(a);
String str3 = Character.toString(a);

Character b = 'b';
String str4 = b+"";
String str5 = String.valueOf(b);
String str6 = Character.toString(b);
String str7 = b.toString();